Research On Power Quality Optimization Of Railway Power Conditioner

In recent years,the rapid development of China's high-speed rail is one of the "four new inventions" of China.It is also a shining business card of China in the international community in the new era,which drives the rapid growth of China's economy.In the extensive use of AC-DC electric locomotives in high-speed railway,due to the application of non-linear and asymmetric loads,a series of power quality problems such as grid current and voltage distortion,three-phase unbalance and so on are caused.When the grid voltage is unbalanced,if there is no compensation device,the harmonic current and negative sequence current generated by it will be injected into the grid,causing grid pollution,and bringing hidden dangers to the safety and stability of the public grid and train.Aiming at the power quality problem of traction power supply system of electrified railway,the main research contents of this paper are as follows.When using the railway static power conditioner(RPC)to solve the problem of power quality in traction power supply system,the compensation current of RPC will increase the voltage fluctuation of the two power supply arms to a certain extent,which may cause the problem of under-voltage or overvoltage in the traction network.Under the premise of guaranteeing the effect of RPC comprehensive management,in order to effectively reduce the RPC compensation capacity and the voltage fluctuation of the two power supply arms as much as possible,in this paper,a RPC multi-objective optimization design method is proposed,which uses the voltage fluctuation degree of the power supply arm and the RPC compensation capacity as the optimization target.In this paper,the reasons for the increase of the voltage fluctuation of the two power supply arms by the RPC compensation current are analyzed,and the voltage fluctuation index of the power supply arm is introduced.The multi-objective optimization mathematical model of RPC is established,and the multi-objective optimization algorithm of particle swarm optimization is used to solve the problem.The effectiveness of the proposed method in reducing the voltage fluctuation of the two power supply arms and reducing the RPC compensation capacity is verified by a numerical example and a experiment.In order to solve the problem that the negative sequence current increases sharply when the regenerative braking of the train generates huge energy flow into the grid,a railway power conditioner(SC-RPC)based on super capacitor energy storage is proposed.The electrical model of SC-RPC regenerative braking condition is established,and by analyzing its compensation principle,and then the mathematical model of minimum negative sequence current is established under the constraints of voltage fluctuation,power factor,equipment capacity and transformer capacity of two power supply arm.In this paper,particle swarm optimization(PSO)is used to solve the small-scale,multidimensional and nonlinear optimal convergence problem by adaptively adjusting the inertia weight of particles.And the corresponding control strategy is put forward.Finally,simulation results show the effectiveness of the proposed method.